The present invention concerns quickly performed measuring methods of the type employed to ascertain the concentration of one or more polar components in a material otherwise mainly comprised of one or more non-polar or only negligibly polar components. Methods of the type here in question involve the measurement of electromagnetic waves transmitted through the material of interest.
Determining the concentration of polar components in otherwise mainly non-polar or only slightly polar materials extends into an enormous variety of practical applications and fields of technology, as revealed by the last several decades of research and development in this particular area. Techniques for making this type of determination are desired both for situations in which the polar and non-polar components of the material are present in the same state of matter and also for situations in which such components are present in different states of matter. In general, the material to be analyzed with respect to concentration of polar components may be a gas, a liquid, a solid, or a combination thereof.
As well known, it can be particularly difficult to perform such concentration measurements upon the polar components in pourable bulk materials, such as coal, because the magnitude of the measurement signal yielded by conventional techniques in general will exhibit a high degree of dependence upon the size of the constituent particles, grains or chunks of such pourable bulk material. When such bulk materials are involved, measurement of polar-component concentration is most usually performed to ascertain the water or moisture content of the material. Lately, when applications such as this are involved, increasing interest has been exhibited by the art in the use of microwave waveguide technology as the means for establishing the requisite electromagnetic-wave transmissions and their interactions with polar components of the material.
Especially when the determination of water or moisture content is what is sought, the expression "quick" measurement technique has come to refer to those techniques in which the water or moisture content can be ascertained within a few seconds, compared to other conventional methods requiring substantially longer periods of time for their performance, e.g., methods involving drying ovens and operating on the basis of thermodynamic instead of electrical and electromagnetic principles.
It will be understood that it is already known to attempt to measure the concentration of such polar components in otherwise non-polar materials by measuring the attenuation of transmitted electromagnetic waves attributable to the dipole relaxation of the polar component. It is also known to combine such attenuation measurement with phase-difference or loss-angle measurements, in an attempt to correct for the effect upon the ultimate measurement signal of such factors as the density of the pourable bulk material involved, the thickness of the sample through which the electromagnetic waves are transmitted, the uneveness or irregularity of the boundary surfaces through which the transmitted electromagnetic waves enter and exit the sample, and so forth. In addition to such transmittance (attenuation) measuring techniques, it is also known to resort to reflection and resonance procedures. Also, besides the use of microwave waveguide technology to establish the requisite wave transmissions and dielectric interactions, it is of course even better known to employ more simple capacitive techniques for ascertaining the concentration of a polar component in an otherwise mainly non-polar material.
These various known techniques and approaches exhibit various already recognized disadvantages and limitations, and also certain disadvantages and limitations which will be seen to exist in comparison to the inventive technique to be described.
For example, when proceeding on a simple capacitive basis and utilizing the sample to be analyzed essentially as the dielectric layer for a more or less elementary capacitor structure, the frequency of the electromagnetic energy employed for the measurement cannot be freely increased without limit. Accordingly, it often becomes impossible to operate at frequencies high enough to preclude the onset of undesirable macropolarization phenomena; e.g., in the extreme case, the energy of the radiation employed may be, to an excessive fractional extent, wastefully and confusingly consumed in the work of merely effecting spatial separation of charged constituents of the material in the crude sense of electrostatics, and not be efficiently utilized for the main task of reorienting polar constituents. Also, with such more or less merely capacitive techniques, it is typically difficult to avoid physical and electrical engagement with the material to be analyzed.
When utilizing techniques based upon the reflection of electromagnetic waves, the measurement signal yielded by the technique tends to be mainly determined by wave reflection occurring at the boundary surface to the sample. As a result, it is mainly this part of the sample which interacts with or contributes to the measurement signal, whereas more deeply located parts of the sample tend not to appreciably participate in the interaction. Additionally, of course, the unevenness or irregularity of the sample's boundary surfaces has a very great influence upon the ultimate measurement signal.
When resort is had to resonance techniques, there arises mainly the problem that the size and amount of the sample is necessarily limited by the need to pack it into the limited space within the resonator chamber employed, and in the case of stray-field resonators it is furthermore typically very difficult to avoid physical and electrical engagement with the sample.
For these and other reasons, the conventional techniques which instead mainly rely upon the measurement of the attenuation of transmitted electromagnetic waves can be considered somewhat more advantageous. However, these too, as presently practiced, have their disadvantages:
1. When relying upon the measurement of transmitted-wave attenuation, the prior art has exhibited a consistent prejudice or commitment to the utilization of the frequency range in which the dipole relaxation of the polar components of interest in any particular measurement occur. To the extent that such prejudice is not merely a matter of habit, the usual view is that, in order to achieve a high signal-to-noise ratio in the ultimate measurement signal, the measurement frequency employed should be as close as possible to the maximum-relaxation-loss frequency f.sub.o =1/2.pi..tau., .tau. being the dipole relaxation time of the polar component of interest in whatever specific material is being analyzed. The invention or concept behind such conventional choice of frequency is that the measurement signal be as much as possible dependent upon and affected by energy consumed in the work of irienting or reorienting polar constituents, i.e., so that the measurement signal obtained will be "tied in" as much as possible to the particular physical phenomenon upon which the concentration measurement is actually being based. Of course, when the measurement frequency employed is the maximum-relaxation-loss frequency f.sub.o, i.e., is the reciprocal of the dipole-relaxation time-constant, the amount of power preferentially abstracted from the transmitted electromagnetic wave for the work of dipole orientation becomes great, resulting in a very high power loss, evidenced in a very great attenuation of the transmitted electromagnetic energy. However, because this very high power loss is so directly attributable to the polar component per se, it is generally considered positively desirable and essential. At the same time, because the resulting attenuation of the transmitted energy will be so very high, it is necessary, and therefore generally accepted without conscious dissatisfaction, that the thickness of the sample through which the radiation is transmitted be quite small, typically resulting in the use of a sample which is essentially merely a thin layer of material. Also, and as very well known, water and other polar components of constant interest for such measurements exhibit behaviour which is extremely dependent upon temperature, always necessitating that countermeasures of one type or another be resorted to in order to take such temperature-dependence into account.
2. When the measurement of transmitted-wave attenuation is supplemented by measurement of transmitted-wave delay or phase displacement, in an attempt to generate information which can be used to correct the attenuation measurement for factors such as sample thickness, density and so forth, this does not per se serve to eliminate the just explained shortcomings of the attenuation measurement per se. Also, when the material of interest is a pourable, mainly solid bulk material, such conventional approach presupposes a relatively high degree of uniformity of the size of the constituent particles, grains or chunks.